(Pneumatic) hydraulic control system for an automatic vehicle transmission

ABSTRACT

A .[.pneumatic.]. .Iadd.hydraulic .Iaddend.control system is disclosed for an automatic transmission for a vehicle of the type having a mechanical planetary gear train with hydraulically actuatable gear elements. A manual control valve dependent upon the position of the transmission gear select lever conveys a pressure medium, for actuating a gear shift element associated with the selected gear when said lever is moved to one of the forward gears of the transmission, through a pressure medium line connected between the manual control valve and the gear shift element. The control system comprises a main control valve dependent upon the position of the accelerator pedal for exhausting the fluid in the gear shift element for disengaging the gear shift element in operating states of the vehicle at least when the vehicle is stationary, the transmission gear select lever is moved to the drive position (D), and the accelerator pedal is released.

BACKGROUND OF THE INVENTION

The present invention relates to a .[.pneumatic.]. .Iadd.hydraulic.Iaddend.control system for an automobile automatic transmission of thetype having a mechanical planetary gear train with hydraulicallyactuated gear shift elements for shifting of the transmission elements.A manual control valve, dependent upon the position of the transmissiongear select lever (hand operated), conveys a pressure medium when one ofthe forward gears is engaged for actuating a gear shift element (forwardgear clutch) associated with the gear.

In automatic hydrodynamic-mechanical transmission, the turbine of thehydrodynamic torque converter is normally connected positively with thedrive gears, when one of the forward gears is selected, by a so calledforward gear clutch. Even during idle, however, the engine transmitshydraulic energy through the convertor pump to the turbine wheel so thatmovement is produced which causes the vehicle to crawl, i.e. to travelslowly forward even though the accelerator pedal is released. Usually,then, in the case of automatic transmissions, the brake must be employedto keep the vehicle stationary or the gear select lever must be moved inthe neutral position.

Crawling of the vehicle during idling may also be eliminated byproviding a special clutch arranged between the turbine wheel and engineactuated by an electrical idling switch. An additional clutch of thistype, however, requires considerable space and is costly.

SUMMARY OF THE INVENTION

The present invention is a .[.pneumatic.]. .Iadd.hydraulic.Iaddend.control system for an automobile automatic transmission of thetype having a mechanical planetary gear train with hydraulicallyactuatable gear shift elements in which the transmission of engine forceduring idling, which produces crawling when one of the transmissionforward gears is engaged, is automatically interrupted.

More particularly, in accordance with the present invention a manualcontrol valve dependent upon the position of the transmission gearselect lever conveys a pressurized first fluid through a pressure mediumline, when one of the forward gears is engaged, to actuate a gear shiftelement (forward clutch) associated with the selected gears. A maincontrol valve, dependent upon the position of the accelerator pedal, isarranged between the manual control valve and the gear shift element andacts to interrupt the delivery of the first pressurized fluid to theelement, and at the same time exhaust the fluid in the gear shiftelement, thereby to disengage the forward clutch, at selected operatingstates of the vehicle at least when the vehicle is stationary, the gearselect lever is in the drive (D) position, and the accelerator pedal isreleased. The control valve may also be coupled to other engineoperating parameters and may be controlled in response, for example, tothe speed of the vehicle or the position of the gear select lever, asdescribed below.

In the preferred embodiment, the main control valve includes a pistonwhich is acted on by a spring in opposition to an accelerator pedalposition-dependent second fluid pressure, .[.preferably air.].. Thepiston is moveable between a first position when the spring force isgreater than the accelerator pedal position-dependent second fluidpressure, in which the pressure medium line leading to the gear shiftelement is connected with a pressure medium outlet to release theforward clutch, and a second position when the force on the piston ofthe accelerator pedal position-dependent second fluid pressure exceedsthat of the spring. In the second position, the pressure medium lineleading to the gear shift element is connected to the pressure line fromthe manual control valve for supplying hydraulic fluid under pressure tothe element to actuate the forward gear clutch.

The piston is provided with a first piston surface at one end acted onby the spring and a second piston surface at its opposite end acted onby the accelerator pedal position-dependent second fluid pressure. Thesecond piston surface is connected by a pressure line which over athrottle point is connected with a pressure line providing an engineload-dependent pressure. The pressure in this line, which is utilized invarious points of the control system of a customary hydrodynamicmechanical transmission, will also vary essentially with the position ofthe throttle valve of the vehicle and thus the position of theaccelerator pedal such that the second piston surface is acted on by apressure which is dependent upon the accelerator pedal position.

Thus, in idling states of the engine, the pressure in the engine loaddependent pressure line decreases, and thus the second fluid pressuredecreases to provide less force in opposition to the spring on thecontrol valve piston. The spring, therefore, will tend to push thepiston toward the first position interrupting the flow of fluid to thegear shift element and exhaust the fluid in the gear shift element todisengage the clutch. Some pressure, however, will still be present (aso-called zero gas.Iadd.pedal postion .Iaddend.pressure) in the engineload dependent pressure line. To assure, therefore, that at idling, whenthe accelerator pedal is released, a complete release of a forwardclutch is obtained, the engine load-dependent pressure line is connectedwith a purging control valve, actuatable by the accelerator pedal, whichmay be incorporated into a conventional kick-down valve. When theaccelerator pedal is released, the purging valve vents the pedalposition-dependent pressure line so that the second fluid pressure,acting on the piston in opposition to the spring, is reduced to zero(atmospheric).

The purging control valve has a control piston displaceable in alongitudinal bore in a piston valve. The accelerator pedal acts on thecontrol piston such that when the pedal is released, the engineload-dependent pressure line is connected to a pressure medium outlet(atmosphere). Thus, when the accelerator pedal is released, the pressurein the line acting on the main control valve is atmospheric. When theaccelerator pedal is at least partially depressed, the pressure mediumoutlet is blocked by the control piston and the engine load-dependentpressure is again provided to act on the piston of the main controlvalve. The purging control valve may be arranged so that the connectionwith the pressure medium outlet is blocked when the accelerator pedal isonly slightly depressed.

At times when the accelerator pedal is released, and the presssure inthe line leading to the main control valve drops to atmospheric, athrottle in the engine load-dependent line prevents the pressure in thatline from dropping to atmospheric upstream of the throttle.

It may not be desirable to disconnect the forward gear clutch, when theaccelerator pedal is released, for all operating states of the vehicle,for example, when the vehicle is operated in mountainous regions orunder special load conditions. In hilly regions, by keeping the forwardgear clutch engaged, the creeping movement of the vehicle during idlingmay be used for starting on hills. Also, it may be desired to use enginebraking which would be lost were the forward gear clutch to be released.Thus, in accordance with the invention, when the gear select lever ismoved to selected positions, e.g. "1" or "2", pressure is automaticallyprovided to the main control valve piston to overcome the force of thespring such that the forward gear clutch remains engaged independent ofthe position of the accelerator pedal. This may be achieved by athree-way valve inserted into the accelerator pedal-dependent pressureline leading into the main control valve, which disconnects theaccelerator pedal-dependent line in favor of a line carrying main enginepressure when the gear select lever is in one of the preselectedpositions, so that pressure delivery will not be interrupted when theaccelerator pedal is released.

The control valve may also be controlled as a function of vehicle speedso that the forward gear clutch is disengaged only when the vehicle isstationary and not when the vehicle is decelerating or coasting. Asecond piston surface is provided which is connected to a speeddependent pressure which acts on the piston in the same direction as theaccelerator pedal position pressure, that is, in opposition to thespring. Thus, when the speed dependent pressure is sufficient, that is,the vehicle is traveling at or above a predetermined minimum speed, theforce on the piston overcomes the spring force to maintain the forwardgear clutch engaged regardless of whether any additional pressure isimparted on the piston from the accelerator pedal position-dependentpressure line. A speed dependent pressure source is likewise availablein conventional control systems for hydromechanical transmissions ofthis type.

For a better understanding of the invention, reference is made to thefollowing detailed description of the preferred embodiments of theinvention, taken in conjunction with the drawings of the application.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-section of a control system in accordancewith the invention for providing accelerator pedal position-dependentcontrol of the gear shift element associated with the forward gears; and

FIG. 2 is a schematic sectional view of a portion of a modified controlsystem.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIG. 1, a .[.pneumatic.]. .Iadd.hydraulic .Iaddend.controlsystem is shown for an automobile automatic transmission of the typehaving a mechanical planetary gear train with hydraulically actuatablegear shift elements for optional shifting of the transmission elements.A forward clutch 1 associated with the forward gears of the hydrodynamicmechanical automobile transmission includes a pressure chamber 2 and anactuating piston 3. The pressure chamber 2 is connected with a firstpressurized fluid line 4, which is connected through a main controlvalve 5 to the pressure fluid line 6 coming from a manual control valve,not shown. Connection between the lines 4 and 6 is controlled as afunction of the position of the accelerator pedal of the vehicle by themain control valve 5. The pressure fluid line 6 provides main pressurein all forward gears which means that it carries the highest pressureutilized in the transmission control system produced by the gear pumpand is regulated dependent on engine load by the so-called main pressureslide valve (not shown).

The main control valve 5 has a piston 7 which is loaded by a spring 8acting on the piston collar 26. The force of the spring 8 can beadjusted by an adjustment screw 9 acting on the spring retainer 10. Thespring 8 is opposed by an accelerator pedal position-dependent secondfluid pressure provided through a line 19 to the end face 18 of thepiston collar 17, which acts as a piston surface. The second fluidpressure line 19 is connected over a throttling point 21 with a pressureline 20 which may be connected to a source of second fluid pressurewhich is a function of the engine load, which is also used in thetransmission control, namely, controlled in dependence of the positionof the throttle valve and thereby the accelerator pedal, which pressureis lower than the main pressure.

A second piston surface 12 on the piston collar 11 of the piston 7 isconnected to a source of speed-dependent fluid pressure through apressure medium line 13. Like the accelerator pedal position-dependentpressure. The speed-dependent pressure acts in opposition to the springforce of the spring 8. As in the case of the engine load-dependentpressure, the speed-dependent pressure is available as a governingpressure in customary transmission control systems.

The piston 7 is displaceable from the center position shown in thedrawing either towards the left or towards the right, depending on thespring force and the instantaneous pressure forces from the lines 13 and19, acting in opposition to the spring 8. As the piston 7 moves right orleft, a pair of control edges 23 and 24 on the piston collar 22 connectthe pressure medium line 4 either with the pressure medium line 6 toprovide fluid under pressure to the pressure chamber 2 (to actuate theforward gear clutch 1), or with a pressure medium outlet 25, therebycausing the forward gear clutch 1 to disengage. The clutch 1, therefore,disengages during operating states of the vehicle when the force of thespring 8 exceeds the combined forces on the piston surface 18 (theaccelerator pedal-dependent pressure) and the circular ring-shapedpiston surface 12 (the speed-dependent pressure). The force exerted bythe spring 8 and, the piston surfaces 12 and 18 are chosen such that thespring force of the spring 18 predominates only if the vehicle isstationary or moving at less than a predetermined speed, and if,simultaneously, the accelerator pedal is released.

A purging control valve 30 is also connected to the engine loadpressure-dependent line 20 to assure that when the accelerator pedal isreleased, the pressure line 19 does not continue to transmit pressure tothe piston surface 18 (the idling .[.gas.]. pressure), but rather iscompletely purged through connection with a pressure medium outlet 35.The valve 30 may be a so-called kickdown valve which is provided in theknown transmission control systems, and actuated by an actuation lever40, connected with the accelerator pedal, which engages the valve piston29. The purging valve 30 has a control piston 36 which can be displacedin a longitudinal bore 34 within the normal play associated with theidling position of the accelerator pedal. The longitudinal bore 34 isconnected through transverse bores 33, the end-face clearances 32 of aguide bushing 31, and a housing pocket 28, to a purging line 27, whichin turn communicates with the pressure line 19. One or more transversebores 35 connect the longitudinal bore 34 with atmosphere, to functionas pressure medium outlet. Connection between the outlets 35 and thebore 34 (and thereby the purging line 27) is controlled by an end-facecontrol edge 37 of the control piston 36.

The kick-down valve 30 is connected with a gas .Iadd.pedalposition-dependent .Iaddend.pressure valve, not shown here, deliveringthe gas .Iadd.pedal position-dependent .Iaddend.pressure of the line 20.A spring 43, acting on a spring plate 42 adjustable on a threaded rod 41of the piston 29, pushes the piston 29 of the valve 30 towards the leftin the drawing against the guide .[.bush.]. .Iadd.bushing .Iaddend.31functioning as a stop. The drawing shows the accelerator pedal and theactuating layer 40 connected thereto in the released position. With theaccelerator pedal released, lever 40 also releases the control piston 36and the pressure prevailing in the line 27 displaces the piston 36 tothe left. The pressure medium outlets 35 are thereby opened, so that thepressure in the line 27 and thereby also in the line 19 drops to almostatmospheric pressure. The throttling point 21 in the connection to thegas .Iadd.pedal position-dependent .Iaddend.pressure line 20 preventsthe pressure in the gas .Iadd.pedal position-dependent .Iaddend.pressureline 20 from likewise dropping to atmospheric pressure: rather, thepressure upstream of the throttle 21 remains at the so-called zero(idling) gas .Iadd.pedal position .Iaddend.pressure level.

The purging of the pressure line 19 through the purging line 27 andoutlets 35 assures that when the accelerator pedal is released, thepiston 7 of the main control valve 5 is pushed by the spring 8 to theright against no counterforce on the piston surface 18. Assuming thenthat the vehicle is also stationary and not coasting or decelerating,and that there is little or no speed dependent pressure acting on thepiston surface 12, the piston 7 is moved to the right by the springforce and the pressure medium line 4 is connected with the pressuremedium outlet 25 across the reduced thickness portion of the piston 7between the piston collars 22 and 26. As a result, the pressure mediumchamber 2 of the forward gear clutch 1 is vented and the clutchdisengages. The positive connection between the turbine wheel of thetorque converter and the vehicle wheels is thereby interrupted so that acreeping of the vehicle cannot occur. At the same time, this measureprevents vibrations, which would otherwise be transmitted by the engineover the transmission to the vehicle wheels during idling, from becomingnoticeable.

If the vehicle is moving above a predetermined minimum speed, theforward gear clutch 1 remains engaged regardless of the acceleratorpedal position (released or depressed). The speed-dependent pressure,carried over the pressure medium line 13 to the circular ring-shapedpiston surface 12 of the piston 7, displaces the piston 7 in oppositionto the force of the spring 8 to the left in the drawing. In thisposition of the piston 7, the pressure medium line 4 is connected withthe pressure line 6 from the manual control valve (not shown), such thatthe main pressure conveyed over the pressure line 6 is directed into thepressure chamber 2 of the forward gear clutch 1 to maintain theactuating piston 3 in the engaged position. Once again, this occursindependent of the pressure delivered over the pressure line 19, i.e.,independent of the position of the accelerator pedal, to assure that theclutch 1 is disconnected only during idling, and not during decelerationor coasting.

When the vehicle is stationary, the forward gear clutch 1 is re-engagedonly when the accelerator pedal is depressed past the path of freemovement (play) associated with its idling position. The control piston36 is moved to the right until the stop bolt 38 encounters the piston 29at the end of the longitudinal bore 34 or the lever 40 engages the outerend face of the piston 29 itself, whereby the control edge 37 closes offthe transverse bores 35. Once the outlets 35 are blocked, the .[.gas.].pressure in line 19 builds up again to the zero gas .Iadd.pedal position.Iaddend.pressure, which is already sufficient to displace the piston 7to the left for connection of the pressure medium line 4 with the line6. Accordingly, the closing off of the pressure medium outlet bores 35by means of the control edge 37 of the control piston 36 occurs evenbefore the accelerator pedal is actuated out of its idling position foracceleration of the vehicle engine.

FIG. 2 illustrates a modified form of main control valve actuatable bymeans of the accelerator pedal. In this form, the control piston 36' ofthe purging valve 30 has grooves along the outer periphery, forpermitting the pressure medium to discharge when the control edge 37'moves away from the shoulder 44. Moreover, the piston 36' does not slidedirectly in the longitudinal bore 34' but slides in a bore 45 which hasa larger diameter than the bore 34'. When the accelerator pedal isdepressed in order to overcome the free travel in the idling position,the actuating lever 40 engages the piston 36', and the end-side controledge 37' of the control piston 36' is displaced towards the shoulder 44between the bores 45 and 34' to block the connection between the bore34' and the pressure medium outlets, which may be the open end of thebore 45. The mode of operation of this embodiment corresponds to that inFIG. 1 so that here again, after the free travel associated with theidling position of the accelerator pedal, the connection of the pressureline 19' with the outlet is blocked so that the raised zero gas.Iadd.pedal position .Iaddend.pressure of the gas .Iadd.pedalposition-dependent .Iaddend.pressure line 20 is again present in thepressure line 19. This pressure is sufficient to move the piston 7 ofthe main control valve 5 to the left, as shown in the FIG. 1, so thatthe control edge 23 of the piston collar 22 produces a connection of thepressure medium line 4 with the pressure line 6 to actute the clutch 1.

In the FIG. 2 embodiment, a three-way ball valve 46 is inserted in theline 19. The three-way ball valve 46 is connected by a pressure line 47with a second three-way ball balve 48. Pressure lines 49 and 50, whichopen into the second three-way ball valve 48, provide main pressure byway of the manual control valve, not shown, to the line 19 and therebythe piston 7, whenever the transmission gear select lever is moved topositions "1" or "2" (as opposed to "Drive" (D)). In these select leverpositions associated with specific load operating conditions of thevehicle, the pressure line 19 receives main pressure as a result ofspecial switching of the three-way valves 46 and 48. This pressureassures that the piston 7 of the control valve 5 is always maintained inits left end position, i.e., in the clutch engagement position, when thetransmission gear select lever is in the "1" or "2" position. Thus, atspecific load operating positions of the select gear lever, a "creeping"of the vehicle becomes possible.

Such a delivery of main pressure in one or both load positions "1" or"2" of the gear select lever, by way of the three-way ball valves(which, depending on the preponderance of the pressure in one or theother supply line in each case closes off the other line), may also beinserted into the pressure delivery line 13 so that thecircular-ring-shaped piston surface .[.112.]. .Iadd.12 .Iaddend.of thepiston 7, too, displaces the piston 7 on pressure admission, into theclutch engagement position.

The invention has been shown and described with reference to certainpreferred embodiments thereof. Variations and modifications will beapparent to those skilled in the art without departing from theinventive principles dislosed herein. For example, the control valves30, 30', decreasing the pressure in the pressure line 19 to atmosphericpressure when the accelerator pedal is released, are illustrated asfluid, preferably .[.pneumatic.]. .Iadd.hydraulic.Iaddend., controlledvalves. It is possible, however, to provide here electrical or alsomechanical control apparatus, which when the accelerator pedal is fullyreleased, connects the pressure medium line 19 with a pressure mediumoutlet and which after a predetermined free path has been overcome,i.e., without the engine having terminated its idling operation, blocksoff the pressure medium outlet. All such modifications and variationsare intended to be within the scope of the invention as defined in thefollowing claims.

We claim:
 1. In an automatic transmission for a motor vehicle, having anaccelerator pedal, said transmission having a mechanical planetary geartrain with hydraulically actuatable gear shift elements, a gear selectlever having a plurality of selectable forward drive positions,including automatic forward drive (D), a source of first pressurizedhydraulic fluid, a manual control valve, responsive to the position ofsaid select lever, for supplying said first fluid to a selected gearshift element when said lever is in one of said forward drive positions,and a fluid line communicating between said manual control valve andsaid selected element for delivering said first fluid from said manualcontrol valve to said selected element, a control system for selectivelyinterrupting the supply of said first fluid to said selected element,comprising a main control valve arranged in said fluid line between saidmanual control valve and said selected element for controlling thesupply of said first fluid from said manual control valve to saidselected element, said main control valve being responsive to theposition of said accelerator pedal and controlling the supply of saidfirst fluid to said element to discontinue said first fluid supply andexhaust the fluid from said element to disengage said element inselected vehicle operating conditions, said conditions including whensaid vehicle is stationary, said gear select lever is in automatic drive(D), and said accelerator pedal is released.
 2. A control systemaccording to claim 1, wherein said main control valve means comprisepiston means, spring means acting on said piston means, means forproviding an accelerator pedal position-dependent second fluid pressurefor acting on said piston means in opposition to said spring means, formoving said piston means to a first position when the spring force onsaid piston means exceeds the accelerator pedal position-dependentsecond fluid pressure force for connecting said gear shift element witha fluid outlet and a second position when said accelerator pedalposition-dependent second fluid pressure force exceeds the spring forcefor connecting said gear shift element with said manual control valvefor providing said first fluid under pressure to said gear shiftelement.
 3. A control system according to claim 2, wherein said pistonmeans has a first piston surface acted on by said spring means and asecond piston surface acted on by said accelerator pedalposition-dependent second fluid pressure, and wherein said means forproviding said accelerator pedal position-dependent second fluidpressure includes a source of engine load-dependent pressure.
 4. Acontrol system according to claim 3, further comprising purging controlvalve means for venting the second fluid pressure supplied to saidsecond piston surface when said accelerator pedal is released, andwherein said source of engine load-dependent pressure includes throttle.[.mmeans.]. .Iadd.means .Iaddend.therein.
 5. A control system accordingto claim 4, wherein said purging control valve means comprise a controlpiston displaceable in a longitudinal bore of a piston valve, whereinsaid accelerator pedal engages said control piston when at leastpartially depressed, said control piston having a control edge foropening a connection to a pressure medium outlet when said acceleratorpedal is released and for interrupting said connection when saidaccelerator pedal is partially depressed.
 6. A control system accordingto claim 4 or 5, wherein said vehicle includes a kick-down controlvalve, and wherein said purging control valve means are contained insaid kick-down control valve.
 7. A control system according to claim 1,wherein said forward drive positions include lever positions associatedwith a specific load operation, wherein said control system furtherincludes means for delivering main fluid pressure to a piston surface onsaid piston means for acting in opposition to said spring means whensaid gear select lever is moved to one of said specific load operations.8. A control system according to claim 7, comprising three-way valvemeans for supplying second fluid pressure to said second piston surfacefor selectively connecting said piston with a source of said main fluidpressure when said gear select lever is moved to a positioncorresponding to specific load operation.
 9. A control system accordingto claim 1, further comprising means for controlling said main controlvalve as a function of vehicle speed.
 10. A control system according toclaim 9, wherein said piston means further comprises a third pistonsurface and, wherein said speed control means comprises means fordelivering a speed dependent third fluid pressure for acting on saidthird piston surface for opposing the force of said spring.